1. Technical Field
The present invention relates in general to storage systems, and in particular disk drives. Still more particularly, the present invention relates to a method of fabricating a write head for use with perpendicular magnetic recording.
2. Description of the Related Art
A hard disk drive (HDD) is a digital data storage device that writes and reads data via magnetization changes of a magnetic storage disk along concentric tracks. As application programs and operating systems become longer with more lines of program code, and data files, particularly graphics files, become larger, the need for additional storage capacity on the HDD increases. Since the trend in HDD design is towards the use of smaller, rather than larger, disks, the solution to increasing the storage capacity of magnetic storage disks is to increase the areal density of data stored on the disk.
Currently, there are two main types of magnetic storage on a magnetic disk: longitudinal and perpendicular. FIGS. 1a and b depict these two types of storage. FIG. 1a depicts the older technology of longitudinal recording. Longitudinal recorded bits 100 are stored when a longitudinal write head 102 magnetizes areas of a magnetic disk 104 in an orientation that is longitudinal to a track 118 on the magnetic disk 104. As shown, the magnetic moment of each subsequent recorded bit is opposing, such that each north pole faces a south pole and vice versa. These opposing moments result in a repulsive force, which leads to long-term instability of the magnetized areas, thus leading to eventual lost data. Nonetheless, longitudinal recording has traditionally been the accepted method of storage because of the materials used to fabricate magnetic disk 104 and the technological limitations on how small a pole tip of longitudinal write head 102 can be and still produce enough flux field to write data.
Modern disk fabrication materials have paved the way for perpendicular recording. These disk fabrication materials typically use a cobalt-chromium ferromagnetic thin film on an amorphous ferromagnetic thin film. This combination of materials affords both ultra-high recording performance along with high thermal stability. The concept of perpendicular recording is illustrated in FIG. 1b. Perpendicular-recorded bits 106 are stored on a perpendicular recording medium 108 as anti-parallel magnets in relation to one another in an orientation that is normal (perpendicular) to the surface of the perpendicular recording medium 108. Because the perpendicular-recorded bits 106 obey the pull of magnetic poles, they do not have the repulsive force of longitudinal recordings, and thus the perpendicular-recorded bits 106 are more stable.
While materials used to construct perpendicular recording medium 108 address part of the technological challenge of perpendicular recording, the other challenge is to fabricate a perpendicular write head 110 having a write pole tip 112 whose tip area is small enough to record the perpendicular-recorded bit 106 without overlapping an area reserved for another perpendicular-recorded bit 106. This overlap must be avoided not only for bit areas on a same track 120, but on bit areas on other tracks (not shown) as well. Thus, the aspect ratio (AR) of linear density (bits per inch—BPI) to track density (tracks per inch—TPI) should be controlled at 1:1 (BPI:TPI) or at most 2:1 to avoid adjacent track interference (ATI).
Furthermore, and more technically challenging, the perpendicular write head 110 must be able to produce a magnetic field that is powerful enough to magnetize an area for a perpendicular-recorded bit 106 without overwriting other bit areas or having to be so close to the surface of perpendicular recording medium 108 as to make head crashes likely.
As write pole tip 112 is scaled to tighter dimensions and constrained by the AR requirements described above, the amount of write field coming out at the tip of write pole tip 112 is attenuated and insufficient to magnetize the bit fields.
Two approaches that have been proposed to bring higher write flux to P3's write pole tip 112 are aggressive flare point and aggressive flux guide throat height in shaping layer 116 (P2). Experimental results have shown the tremendous difficulty in implementing aggressive flare point and P2 placement without encountering track-width variation and adjacent track interference (ATI). The ability to simultaneously control both flare point and track-width using ion milling approach is difficult due to the physical nature of this destructive method and the specification targeted. Equally challenging in bringing the flux guide layer closer to the Air Bearing Surface (ABS) are Adjacent Track Issues (ATI). (As is known to those skilled in the art of hard disk drives, as a disk spins under a read/write head, the small space between the read/write head and the disk is maintained by pressure of air passing between the read/write head and the disk surface, creating an “Air Bearing Surface,” or ABS.) The P2 structure is much bigger in area at the ABS view as compared to the write pole. Effective write field, generated by an applied current, would prefer to leak from P2's surface closest to and facing the air bearing surface (ABS) instead of being funneled toward the pole tip. When P2 is brought closer to the ABS, it will bring more fields to the pole tip, but also adversely contribute significantly to ATI issues such as side writing and side erasure.
What is needed, therefore, is a perpendicular write head that has a very small write pole tip that is able to generate sufficient flux fields for magnetizing data bits areas without ATI issues, and a method to manufacture such a write head.